Photosensitive elements which can be used in image-reproduction processes are well-known in the graphics arts industry. Such elements are usually exposed to actinic radiation through an image-bearing transparency, such as a color separation transparency, to produce an image which is either a positive or negative with respect to the transparency used.
Such photosensitive elements are widely used in off-press color proofing to simulate the images produced by printing. In a surprint proof, all of the colored images are superimposed, by, for example, multiple exposure, lamination, or transfer, onto a single support. Unlike an overlay proof, the colored images cannot be separated and viewed individually.
Various processes for producing copies of images involving photopolymerization and thermal transfer techniques are known as disclosed in U.S. Pat. Nos. 3,060,023; 3,060,024; 3,060,025; 3,481,736; 3,574,049 and 3,607,264. In these processes, a photopolymerizable layer coated on a suitable support is imagewise exposed to a photographic transparency. The surface of the exposed layer is then pressed into contact with the image receptive surface of a separate element, and at least one of the elements is heated to a temperature above the transfer temperature of the unexposed portions of the layer. The two elements are then separated, whereby the thermally transferable, unexposed, image areas of the composite, transfer to the image receptive element. If the element is not precolored, the tacky, unexposed image may now be selectively colored with a desired toner. All of these processes necessitate the use of specially treated final receptor sheets and are not applicable for obtaining a color proofing image on a paper stock.
If the element is precolored, flexibility in the choice of colors is limited because preparation of the precolored elements in all the desired colors is not economically feasible. Toning provides greater color flexibility.
U.S. Pat. No. 5,534,387, issued Jul. 9, 1996, discloses a process for forming a colored image, said process comprising, in order: applying at least one aqueous permeable colorant-containing composition to a photosensitive element comprising, in order, a carrier element having a release surface, said carrier element being resistant to aqueous liquid development, a first adhesive layer, an unpigmented, first photosensitive layer consisting essentially of an aqueous liquid developable photosensitive composition, wherein the aqueous permeable colorant-containing composition is in contact with the first photosensitive layer, wherein the aqueous permeable colorant-containing composition is applied the unpigmented photosensitive composition. After imagewise exposing to actinic radiation, the photosensitive element having applied thereon the permeable colorant-containing composition results in imagewise exposed and unexposed regions in the unpigmented, first photosensitive layer and the overlying permeable colorant-containing composition. The element is then developed thereby removing either the imagewise exposed or imagewise unexposed regions, to produce a first colored pattern. A transfer element having a release surface is then laminated to the element having the first colored pattern, wherein the release surface is adjacent to the first colored pattern. The carrier element is then removed, revealing the adhesive layer. This element is then laminated to the permanent substrate and the transfer element having a release surface is peeled off to leave a single color image on the permanent substrate. A process for forming a multicolor image is also disclosed. This process provides the color flexibility, but the time needed to prepare these proofs is longer than that required to form a laser induced thermal image. Further, since this is an analog process it requires the use of separation transparencies which have to be redone each time a color change is required.
Laser-induced thermal transfer processes are well-known in applications such as color proofing and lithography. Such laser-induced processes include, for example, dye sublimation, dye transfer, melt transfer, and ablative material transfer. These processes have been described in, for example, Baldock, U.K. Patent 2,083,726; DeBoer, U.S. Pat. No. 4,942,141; Kellogg, U.S. Pat. No. 5,019,549; Evans, U.S. Pat. No. 4,948,776; Foley et al., U.S. Pat. No. 5,156,938; Ellis et al., U.S. Pat. No. 5,171,650; and Koshizuka et al., U.S. Pat. No. 4,643,917.
Laser-induced processes use a laserable assemblage comprising (a) a donor element, and (b) a receiver element that are in contact. The laserable assemblage is imagewise exposed by a laser, usually an infrared laser, resulting in transfer of material, ie., the exposed areas of the thermally imageable layer, from the donor element to the receiver element. The (imagewise) exposure takes place only in a small, selected region of the laserable assemblage at one time, so that transfer of material from the donor element to the receiver element can be built up one pixel at a time. Computer control produces transfer with high resolution and at high speed. The laserable assemblage, upon imagewise exposure to a laser as described supra, is henceforth termed an imaged laserable assemblage.
Laser-induced processes are generally faster than analog processes and result in transfer of material with high resolution areas.
A need exists for combining the high resolution and speed afforded by laser induced processes with the color versatility afforded by analog systems.